The present invention relates to the tightness around tubes.
In particular, but not exclusively, the invention relates to the tightness around transfer tubes of nuclear power plants.
As shown in FIG. 1, a nuclear power plant generally comprises a reactor building 4 containing a primary circuit C1 and the nuclear reactor 5. Fuel rods, in which fission products are confined, are arranged in the form of assemblies in the reactor 5.
The subsequent fission creates heat. Pressurized water is used as coolant. The water contained in the primary circuit C1 transmits its heat to water contained in a secondary circuit C2. This heat exchange is carried out using one or more steam generators GV.
Once heated, the water of the secondary circuit C2 turns into steam. This high-pressure steam turns a turbine driving an alternating current generator which produces electricity. After passing through the turbine, the steam is re-cooled, turned back into water, and returned to the steam generator(s) GV for a fresh cycle.
A fuel building 6 also adjoins the reactor building 4. A space between concrete containment walls 3 acts as a separator between these two buildings. The fuel building 6 contains a cooling pond 7. The latter, which is filled with water, receives the spent fuel from the reactor building 4 for a period sufficient to allow the fuel assemblies to cool.
Spent fuel is transferred between the reactor building 4 and the fuel building 6 using a connecting tunnel called a “transfer tube”. This transfer tube 1 therefore crosses the space between concrete containment walls 3 and opens at one of its ends (on the left in FIG. 1), into the water of the cooling pond 7. Its other end (on the right in FIG. 1) opens into a generally submerged part of the reactor building 4.
In order to protect the transfer tube 1, it is known to use a compensator (not represented in FIG. 1) as well as a tightness collar 2. The latter was fitted during the construction of the power station, by being slid on one of the ends of the transfer tube 1, before the latter is immersed in the water of the cooling pond 7. As shown in FIG. 1, it is placed around a portion of the transfer tube 1 and in contact with the space between the containment walls 3 which act as a separator between the reactor building 4 and the fuel building 6. It is generally placed on the side of the fuel building 6, as shown in FIG. 1. Alternatively, this collar can be placed to seal the transfer tube on the side of the reactor building 4 (reference 2′ in FIG. 1). Two collars can optionally be positioned on either side of the space between containment walls 3.
Such a collar is usually composed of a single block of ethylene and propylene reinforced with fabric, able to withstand up to 20 kg/cm. It is designed not to burst suddenly in case of overpressure, typically of three relative bars.
Although of proven effectiveness, the existing collars can fail or experience a degree of wear. In some cases, the degradation of the collars is linked with the fact that the nuclear power plants in which they are installed are still in service several years beyond their initially scheduled lifespan.
A replacement of the existing collars can therefore be necessary in certain situations. However, the fitting of a new collar to a transfer tube of a power station already in service is not easy, particularly because the ends of the transfer tube are not easily accessible.
Similar problems arise in fields other than that of nuclear power plants. Collars can be used to seal a tube connecting two spaces, at least one of which can contain a fluid (for example sterilized air, gas, contaminated or polluted water, etc) or substances to be confined in this space.
This can be the case for example in factories manufacturing medicaments, heating networks (waste incineration plants connected to the hot water network), thermal combustion power stations (coal, fuel oil or gas) which include confined spaces crossed by tubes, passage through which must be completely tight and made secure, etc.
An object of the present invention is to propose a collar having the required properties for sealing a tube and which is relatively easy to install in a location already in service.